My current theory is this: Satoshi works for some three-letters government agency or massive orgnaization with extremely deep pocket, the reasons are listed below.
1. Intelligence agencies such as NSA are known to employ some of the world's best cryptographists, and the job requires you to consider every possible threat and make things bullet-proof, the kind of meticulousness we saw in the Bitcoin protocol.
2. Satoshi went to such great length to conceal his identity, because if it's made public, he may lose his job. He should have talked to his superiors about what he was doing, and since his pet project involved nothing classified, and even contains something probably useful to the intelligence work, he got a "go ahead", but on the condition that he kept his identity a secret, for obvious reasons. And needless to say, the revelation of his identity would not put Bitcoin in a good light.
3. Since these government agencies are extremely well-funded, they probably would not care too much about if their employers are always hard at work, so Satoshi got plenty of time to pursue his own ventures.
I think he's just a normal guy but with the mind of a genius. He saw bitcoins getting bigger and wanted to distance himself from it and wasn't interested in fame. He didn't want to be the one behind bitcoins, he wanted the community to fill that role which it has.
